Gas turbine airfoils exposed to hot combustion gases have been cooled by passing a cooling fluid, such as compressed air bled from a compressor of the gas turbine, through a hollow interior of the airfoil to convectively cool the airfoil. Gas turbine airfoils such as vanes may be provided with a cooling fluid to cool the vane but the vane may also be required to conduct a portion of the cooling fluid to cool a downstream element of the turbine. FIG. 1 illustrates a known arrangement for cooling a gas turbine vane 96 and conducting a portion of a cooling fluid downstream. The gas turbine vane 96 depicted in FIG. 1 may include an outer hollow member 98 having a desired airfoil shape exposed to a hot combustion gas 100 and an inner hollow member 102 held spaced inwardly away from the outer hollow member 98 to form a cooling space 104 between the inner and outer members. Typically, the outer hollow member 98 serves as a structural member of the vane 96 and the inner hollow member 102 may be formed as a sleeve for insertion into the outer hollow member 98. The inner hollow member 102 may include a fluid flow path 106 for conducting a cooling fluid flow 108 through the vane 96 to cool a downstream element, such as a turbine blade, using a tangential on-board injection (TOBI) system. In addition, passageways 110 may be formed in the inner hollow member 102 to allow a portion of the cooling fluid flow 108 to exit the fluid flow path into the space 104 between the inner and outer members to cool the outer hollow member 98, such by using the known technique of impingement cooling. The impinged cooling fluid 112 may be allowed to mix in a trailing edge region 114 and then may be directed to exit a trailing edge 116 of the vane 96. In such vane designs, it is important to control the cooling fluid flow through the vane to provide sufficient cooling of the vane, while also providing a cooling fluid flow effective to cool downstream elements, such as a row of blades disposed downstream of the vane 96. One of the problems with such designs is that a distribution and velocity of the cooling fluid flow in the space 104 between the inner and outer members may be difficult to control to achieve a desire cooling effect. Another problem is that a seal (not shown) typically needs to be provided between the inner hollow member 102 and the outer hollow member 98 (such as around the periphery of the inner hollow member 102 near a location where the cooling fluid flow 108 is injected into the vane 96). Such a seal needed to seal the space 104 between the inner hollow member 102 and the outer hollow member 98 to insure that the cooling fluid flow 108 flows within the inner hollow member 102 before being allowed to exit the fluid flow path 106 through the passageways 110 into the space 104. Furthermore, for gas turbine vanes having a complex shape, such as a twisting or bending geometry along a radial axis, it may be difficult to fit the vane with an inner member formed as an insertable sleeve.